The ultimate goal of the proposed study is to increase the safety of mechanically ventilated (MV) tube-fed patients. This group is at high risk for aspiration of regurgitated gastric contents with deleterious consequences including transient hypoxemia, chemical pneumonitis, and potentially life-threatening nosocomial pneumonia. Efforts are made in practice settings to detect aspirations early so that interventions can be initiated to prevent morbidity and mortality. However, clinicians are unsure about how to accomplish this since currently available bedside methods to detect aspirations are unreliable. A laboratory method of detecting aspirations based on pepsin was tested in an animal model in the current study (8/1/99-7/31/02) and found to be highly sensitive and specific. Preliminary studies have indicated that the laboratory assay can detect pepsin (a proxy for the aspiration of gastric contents) in tracheal secretions suctioned from critically ill tube-fed patients. To determine the extent to which pepsin in tracheal secretions predicts the development of pneumonia, daily Clinical Pulmonary Infection Scores will be calculated. Another problem in the management of tube-fed MV patients is uncertainty about how to assess for significantly slowed gastrointestinal (GI) motility, a condition that predisposes to aspiration. Especially problematic is difficulty in determining when indicators of slowed GI motility, such as large GI residual volumes, are of sufficient magnitude to warrant temporary withholding of feedings. As a result feedings are often withheld unnecessarily, leading to significantly reduced caloric intake. Therefore, another aim of the proposed study is to identify the signs of slowed GI motility that are most predictive of aspirations of gastric contents. Additional aims are to examine the effect of risk factors for aspiration on the detection of pepsin in tracheal secretions as well as the effect of risk factors for pneumonia on the development of pneumonia. The proposed work is a prospective, descriptive study of 680, critically ill, tube-fed patients who will be monitored 24 hours a day for the first 3 days of tube feedings to assess for: pepsin in suctioned tracheal secretions, signs of GI intolerance to tube feedings (large GI residual volumes, absence of bowel sounds, and presence of vomiting), and risk factors for aspiration and pneumonia. In addition, Clinical Pulmonary Infection Scores will be calculated daily for the first 4 days of tube feedings. Patients will be recruited from 5 intensive care units at a Level I trauma center. Data collection will occur over a 24-month period and the data will be analyzed by logistic regression and multiple linear regression.